There was a problem with your code.. a space in $product.m anufacturerid. Anyway, I put it in a "if" statement just in case the manufacturer is undefined in some products.
Code:
{if $product.manufacturer ne ""}
Other products from <a href="manufacturers.php?manufacturerid={$product.manufacturerid}"><b>{$product.manufacturer}</b></a>
{/if}
It seems to work just fine. Thanks